Im going to assume you are talking about a graphics card. I really have no clue if it is possible.
By flashing the bios on the graphics card, you are voiding your warranty for one. 2nd, you are at risk of bricking the card and turning it into a paperweight.
My GTX780 6GB has a custom bios. Completely different bios version from what came with the GTX780 3GB versions. I would never attempt to flash a 3GB cards bios onto my card, as the risk of bricking a card that i paid $500 for is just too great.